Wideband multi-channel receivers for wireless communications base stations is an emerging technology with the potential to increase network capacity and quality. These wideband receivers are capable of digitizing the entire spectrum designated for reverse link communications. The digitized spectrum contains the signals present on all the frequency channels in use for a frequency-division multiple access system. Each base station then selects and digitally processes those frequency channels which are assigned to that particular base station. The frequency channels processed by the base station are easily re-configured with software commands, allowing for base station frequency assignments to be changed easily, and even dynamically, in response to the changing load in the cellular system.
One potentially serious problem with the use of wideband receivers for wireless communications systems is that of receiver dynamic range limitations. Because the receiver must typically provide an equal amount of RF amplification to each of the frequency channels in the allotted cellular frequency band prior to the signal being applied to its analog to digital converter (ADC), it can be difficult to adequately process all of the desired channels if a large received power difference exists between the strongest and the weakest signals. For example, consider a wideband base station receiving signals from two mobile units in its cell, with one unit located very near the base station receiving antenna and one unit at the cell boundary, far from the base station receiving antenna. The difference in received signal power between the two users in likely to exceed 60 dB and may be as large 90 dB. Such scenarios are often referred to as the "near-far problem". If the gain of the receiver is adjusted so that the strong signal causes the ADC to output its full scale value, and if the instantaneous dynamic range of the receiver is insufficient, the weak signal is lost amid the ADC quantization noise and receiver's additive noise. Conversely, if the gain of the receiver is adjusted so that the weak signal is amplified above the receiver noise floor, and if the instantaneous dynamic range of the receiver is insufficient, the strong signal saturates the receiver's analog components and/or the ADC causing nonlinear distortion for all received channels. If the power level difference between the strongest signal and the weakest signal is 90 dB and a signal to noise ratio of 18 dB must be preserved for the weak signal, the wideband receiver would require an instantaneous dynamic range of at least 108 dB. In practice, an instantaneous dynamic range greater than 80 dB dynamic range is difficult to achieve. As a result, existing base station receivers lack the ability to compensate for the gain required to receive inbound signals from near and far mobile units.